Synthesis and structure of a palladium(II) chloride complex with 2-(2-methyl-3-phenyl-isoxazolidin-5-yl)-pyridine

Article abstract of DOI:10.1515/znb-2000-0505

The 1:1 complex of palladium(II) chloride with 2-(2-methyl-3-phenyl-isoxazolidin-5-yl)-pyridine (L) has been prepared and studied by means of elemental analysis, ¹H NMR spectroscopy and X-ray diffraction (monoclinic, space group P2₁/n with parameters: a = 8.141(2), b = 9.750(2), c = 20.691(6) A, β = 95.62(3)°, V = 1634.4(7) A³, Z = 4; R1 = 0.054 and wR2= 0.144 for 3352 unique reflections). A square-planar coordination polyhedron has been established for the palladium atom both in acetone solution and in the solid state. The organic ligand is coordinated to metal in a bidentate manner via nitrogen atoms of the pyridine substituent (Pd-N(2) 2.125(3) A) and the isoxazolidine heterocycle (Pd-N(1) 2.102(3) A). The other two coordination positions of palladium are occupied by chlorine atoms (Pd-Cl(1) 2.321(1) and Pd-Cl(2) 2.333(1) A). The six-membered chelate ring formed by Pd, N(2), C(4), C(1), O(1) and N(1) possesses a twist-tub conformation. The isoxazolidine cycle has an envelope conformation with an equatorial orientation of the methyl group.

Full text of DOI:10.1515/znb-2000-0505

Synthesis and Structure of a Palladium(II) Chloride Complex with
2-(2-Methyl-3-phenyl-isoxazolidin-5-yl)-pyridine
Andrey B. Lysenko3, Oleg V. Shishkin*3, and Rostislav D. Lampeka3
3 Department of Inorganic Chemistry, Kiev University,
Vladimirska St. 64, Kiev 252033, Ukraine
b Scientific Research Department of Alkali Halide Crystals, STC “Institute for Single Crystals”,
Lenina S t., 60, 310001 Khar'kov, Ukraine
Reprint requests to Dr. R. D. Lampeka. E-mail: R.lampeka@clariant.webber.net.ua
Z. Naturforsch. 55 b, 373-376 (2000); received December 22, 1999
Isoxazolidines, Palladium(II) Complexes, IR Data
The 1:1 complex of palladium(II) chloride with 2-(2-methyl-3-phenyl-isoxazolidin-5-yl)-
pyridine (L) has been prepared and studied by means of elemental analysis, 1H NMR spec-
troscopy and X-ray diffraction (monoclinic, space group P2i/n with parameters: a = 8.141(2), b
= 9.750(2),c = 20.691(6)A ,ß = 95.62(3)°,V = 1634.4(7)A ,Z = 4;R 1= 0.054andwR2= 0.144
for 3352 unique reflections). A square-planar coordination polyhedron has been established for
the palladium atom both in acetone solution and in the solid state. The organic ligand is coor-
dinated toometal in a bidentate manner via nitrogen atoms of the pyridine substituent (Pd-N(2)
2.125(3) A) and the isoxazolidine heterocycle (Pd-N(l) 2.102(3) A). The other two coordina-
tion positions of palladium are occupied by chlorine atoms (Pd-Cl(l) 2.321(1) and Pd-Cl(2)
2.333(1) Ä). The six-membered chelate ring formed by Pd, N(2), C(4), C(l), 0(1) and N(l)
possesses a “twist-tub” conformation. The isoxazolidine cycle has an envelope conformation
with an equatorial orientation of the methyl group.
Introduction
Isoxazolidine derivatives attract considerable at-
tention as intermediates in organic synthesis [1].
Moreover, these substances display a wide spectrum
of biological activity including pesticide, herbicide
and anti-cancer properties [2 -4 ].
I
II
influence on the relative stability of the isoxazo-
lidine compounds. This report is the first attempt
regarding this topic.
To establish the peculiarities of isoxazolidine ring
coordination to “soft” Pirson acids we have stud-
ied the palladium(II) dichloride complex with 2-
(2-methyl-3-phenyl-isoxazolidin-5-yl)-pyridine as
a ligand.
Isoxazolidines are also interesting ligands in co-
ordination chemistry. The presence of neigbouring
a -donor heteroatoms (N-O) enables one to prepare
complexes with several types of coordination.
3,5-Disubstituted isoxazolidines are character-
ized by the presence of stereocenters and a five-
membered kinetically labile ring which cause the
existence of stereoisomers and conformers. The co-
ordination of a 5-(2-pyridyl) substituted isoxazoli-
dine to a metal ion, especially with participation
of the isoxazolidine heteroatoms in N,N- or N ,0-
chelating manners, may stabilize one of the con-
formers of the isoxazolidine ring.
Experimental
Preparation of ligand and palladium complex
The starting materials for the synthesis of 2-(2-methyl-
3-phenyl-isoxazolidin-5-yl)-pyridine (L) were commer-
cially available benzaldehyde, N-methylhydroxylamine
hydrochloride and 2-vinylpyridine. The N-methyl-C-
phenylnitrone was prepared as described [8] (m. p. 84-
85°C). The ligand L has been obtained by standard
1,3-dipolar reaction of N-methyl-C-phenylnitrone with
Although there are several reports on X-ray stud-
ies of arene and carbonyl complexes of Cr and W
with isoxazolidines [5 -7 ], these investigations did
not illustrate how the coordination may have an
K
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374
A. B. Lysenko et al. ■Palladium(II) Chloride Complex
Toluene
95*C
70h
V
- +
N - 0
/
Table 1. Crystallographic data for [Pd(L)Cl2].
Table 2. Selected bond lengths (A) and angles (°) for
structure of [Pd(L)Cl2],
Formula
C15H16Cl2N20Pd
417.60
monoclinic
Pd(l)-N(l)
Pd(l)-N(2)
Pd(l)-Cl(l) 2.321(1)
Pd(l)-Cl(2)
0(1)-C(1)
0(1)-N(1)
Formula weight
Crystal system
Space group
a [A]
b [A]
c [A]
2.102(3)
2.125(3)
1.497(5)
1.518(5)
1.523(5)
1.561(6)
1.545(6)
N(l)-C(15)
N(l)-C(3)
C(l)-C(4)
C(l)-C(2)
C(2)-C(3)
P2,/n
2.333(1)
1.452(5)
1.465(4)
8.141(2)
9.750(2)
20.691(6)
95.62(3)
1634.4(7)
4
1.697
18.93
832
/? [°J3
N(l)-Pd(l)-N(2) 92.2(1)
N(l)-Pd(l)-Cl(l)
N(2)-Pd(l)-Cl(l)
0(1)-N(l)-Pd(l) 110.4(2)
C(15)-N(l)-Pd(l) 112.2(2)
U [A3]
88.7(1)
Z
173.6(1) C(3)-N(l)-Pd(l) 109.6(2)
Dcalc [g cm“3]
//(Mo-Ka) [cm-1]
F(000)
Data collection
20max [°]
Index ranges
N(l)-Pd(l)-Cl(2) 174.86(8) C(8)-N(2)-C(4)
117.4(3)
C(8)-N(2)-Pd(l) 120.6(3)
92.4(1)
87.10(4)
105.0(3) 0(1)-C(1)-C(4)
N(2)-Pd(l)-Cl(2)
Cl(l)-Pd(l)-Cl(2)
C(l)-0(1)-N(l)
0(1)-N(1)-C(15) 104.0(3) 0(1)-C(1)-C(2)
0(1)-N(1)-C(3)
C(15)-N(l)-C(3) 117.5(3) N(l)-C(3)-C(2)
121.7(2)
108.6(3)
105.0(3)
104.5(3)
100.7(3)
C(4)-N(2)-Pd(l)
60.1
0< h <15, 0< k <13,
-29< / < 29
5353
102.5(3) C(3)-C(2)-C(l)
Reflections collected
Unique data
4726
of palladium complex was 0.200 g (~70%). It is read-
ily soluble in chloroform, dichloromethane, acetone, ace-
tonitrile and practically insoluble in hexane. Analysis for
[Pd(L)Cl2]: Ci5Hi6Cl2N2OPd (Mr = 417.60): Calcd C
43.14, H 3.86, N 6.71. Found C 43.6, H 3.9, N 6.6%.
The IR spectrum of liquid L as thin film between KBr
discs was recorded on a UR-10 (Carl Zeiss, Jena) spec-
trometer (400-4000 cm-1).
’H NMR spectra of the ligand (CDCI3 ) and the com-
plex (acetone-dö) were obtained on a Bruker WP-100
(100.1 Hz) at 293 K using tetramethylsilane (TMS) as an
internal standard.
0.055
^int
Structure refinement
Data used [I > 2cr(I)]
Parameters refined
Data to parameters ratio
R1
Rw
GOF on F2
Largest peak in finalo
difference map [e A-3]
3352
208
16.12
0.054
0.130
0.986
1.11
freshly distilled 2-vinylpyridine (bp 80-82°C/29 mm) [8]
according to scheme above.
The mixture of products was separated by means
of column chromatography on silica gel with aceton-
chloroform (1:3) as an eluent. The yield of L (oil) was
~65%.
Crystal structure determination
All crystallographic measurements were made at 293 K
using a four circle Siemens P3/PC automated diffrac-
tometer with graphite-monochromated Mo-KQ radiation
(A 0.71073 A). An orange prismatic single crystal of the
demensions 0.5 x 0.1 x 0.1 mm was used.
The palladium complex has been synthesized from
commercial Na2[PdCU] in accordance with scheme:
Na2[PdCl4] + L — [Pd(L)Cl2] + 2NaCl
The structure was solved by direct methods by us-
ing the SHELXTL-PLUS set of programs [9]. H atoms
were placed at calculated positions and refined isotropi-
cally. The structure was established by full-matrix least-
square calculations with an anisotropic approximation for
all non-hydrogen atoms to an R\ value of 0.054 (wR2=
0.144,3352 reflections, F > 4cr(F), S = 0.986). Table 1lists
details of cell parameters, data acquisition and structure
L (0.163 g, 0.68 mmol) dissolved in 5 ml of warm
methanol was added dropwise to a mechanically stirred
solution of Na2PdCl4 (0.200 g, 0.68 mmol) in 6 ml
of methanol. The yellow solution was stirred at r.t. for
1 h. The yellow precipitate was filtered and recrystal-
lized from acetone-chloroform (1:1). The yellow residue
was dried additionally in vacuo at ~ 50°C. The yield
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A. B. Lysenko et al. ■Palladium(II) Chloride Complex
375
Fig.l. Molecular structure of [Pd{2-(2-methyl-3-phenyl-isoxazolidin-5-yl)-pyridine}Cl2].
manner via two nitrogen atoms. This was confirmed
by the X-ray study.
refinement. Selected geometric parameters of [Pd(L)Cl2]
are listed in Table 2. Full crystallographic data have been
deposited at the Cambridge Crystallographic Data Cen-
ter and may be obtained by quoting the number CCDC
136771.
D escription o f the structure
The [Pd(L)Cl2] complex has a molecular ar-
ray. The crystal lattice consists of the racemate of
[Pd{(3R,5R)-2-(2-methyl-3-phenyl-isoxazolidin-
5-(yl)-pyridine}Cl2] and [Pd{(3S,5S)-2-(2-methyl-
3-phenyl-isoxazolidin-5-(yl)-pyridine}Cl2]. There
is a short contact between neighbouring molecules
forH(10)[C(10)]- • Cl(2)2.82 A (1.5-jc,y-0.5,0.5-z)
(the sum of van-der-Waals radii being 3.06 A). The
palladium atom has a nearly square planar environ-
ment (torsion angle N(1)-C1(1)- N(2)-C1(2) - 7°).
It is bonded to two nitrogen atoms of the ligand
and two chlorine atoms. In contrast to X-ray data
for related structures [11 - 14], the Pd-N(pyridine)
bond is longer than (Pd-N (isoxazolidine nitrogen
atom) (Pd-N (l) 2.102(3) A, Pd-N(2) 2.125(3) A)).
An analogous pattern is observed when palladium
is coordinated via the nitrogen atoms of pyridine
and C=N azomethine groups [15 - 17].
Results and Discussion
The IR spectrum of L shows characteristic strong
absorptions at 2990 - 3095 (V(C-H)) and 1500 -
1600 cm -1 (^(C=C) of the aromatic groups) and at
2770-2915, 1335-1470 M C -H ) and <5(C-H) of the
aliphatic groups).
In the 1H NMR spectrum of L the signal of C5H is
located at b 5.35 (dd). Thus the 1,3-dipolar reaction
is highly regioselective and gives 3,5-disubstituted
isoxazolidine [10].
The ‘H NMR spectrum of [Pd(L)Cl2] shows
some interesting features. The shifts of protons C5H,
C3H, CH3-N and a-pyridine groups were found at
lower field as compared with the corresponding 1H
NMR shifts of isoxazolidine in L (ppm, b\ C5H
5.35, C3H 3.75, CH3 2.69, a-py 8.57 for L; C5H
6.00, C3H 4.25, CH3 2.87, a-py 9.50 for complex).
Therefore, we concluded that the organic ligand was
coordinated to the palladium atom in a bidentate
The distances 0(1)-N (1), N(l)-C(3), N(2)-C(8),
N(2)-C(4) (1.465(4), 1.518(5), 1.354(5), 1.364(5)
A) are longer than their averages seen in organic
molecules (1.438, 1.469, 1.337, 1.337 A[18]) as a
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A. B. Lysenko et al. ■Palladium(II) Chloride Complex
376
idine ring is almost coplanar to the C (l)-H (l) bond
with a torsion angle H (l)-C (l)-C(4)-C (5) of 11.3°.
The methyl group has equatorial orientation [torsion
angle C(15)-N(l)-C(3)-C(2) 157.1(3)°], while the
phenyl group is situated axially [torsion angle C (l)-
C(2)-C(3)-C(9) 97.7(4)°].
Thus we may conclude that 5-(2-pyridyl)-sub-
stituted N-methyl isoxazolidines can act as N,N
donor bidentate ligands for “soft” palladium(II)
cation. The six-membered chelate ring stabilizes
an envelope conformation of the isoxazolidine ring
with an equatorial orientation of the methyl group.
result of the coordination of the nitrogen atoms to
the metal atom .C (l)-C (2) (1.561(6) A) and C(3)-
C(9) (1.536(5) A) are also longer than the averages
found for related system (1.521 and 1.513 A [18]).
The six-membered chelate ring formed by Pd,
N(2), C(4), C (l ), 0(1), N (l) has a twist-tub confor-
mation. The atoms 0(1) and N (l) deviate by 1.15
and 0.59 A, respectively, from the mean plane of
the atoms PdN(2)C(4)C(l).
The isoxazolidine ring has an envelope confor-
mation. The deviation of N (l) from the mean plane
of atoms C(3)C(2)C(1)0(1) is 0.67 Ä. The pyr-
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